1. Field of the Invention
The present invention relates to an imageable element, including a substrate, a crosslinked layer disposed on the substrate and an imageable ink-receptive layer disposed on the crosslinked layer. More particularly, the present invention relates to an imageable element, wherein the imageable ink-receptive layer includes an ablation free imageable composition.
2. Description of the Prior Art
It has been known for some time that water-in-oil emulsions are formed when lithographic inks encounter fountain solution in the nips between the plate cylinder and the ink form rollers. In fact, a substantial amount of water can be emulsified in this fashion during normal printing (about 15-20%) (P. J. Hartsuch, Chemistry of Lithography, 2nd Ed., 248, (1960)).
The study of in situ lithographic emulsions and the associated implications for print quality has been going on for almost as long (see J. S. Lavelle, W. D. Schaeffer and A. Z. Zettlemoyer, PRIA Preceedings, Rome, (1969)).
The presence of in situ ink emulsions does not necessarily detract from the performance of any given lithographic ink as long as a separate fountain solution can be used to balance printing properties. On the other hand, the industry as long sought an alternative to using fountain solution to moderate the printing process without having to resort to expensive press modifications and/or non-commercial printing plates. The notion that an ink emulsion (i.e. so called single fluid ink) might possibly deliver both hydrophilic and oleophilic phases to the printing plate in the absence of fountain solution naturally follows from the knowledge gained from the study of in situ ink emulsions. However, asking an ink emulsion to do the work of ink and fountain solution is a rather tall order.
Some of the potential industrial solutions to this challenge can be gleaned from the patent literature. Recently, Kingman et al. published U.S. Pat. No. 6,140,392 that disclosed a lithographic ink composition including acid-functional vinyl polymer and a polyol phase (K. P. Kingman, R. A. Balyo and M. V. Oberski, U.S. Pat. No. 6,140,392, (2000)).
They claim that this particular composition can be used in lithographic printing without fountain solution. Kingman et al. disclosed the specific use of an acid functional vinyl polymer in the ink-receptive continuous phase of an ink emulsion.
The xe2x80x9cvinylxe2x80x9d polymer described in the patent is a relatively low molecular weight copolymer of styrene, stearyl methacrylate, butyl acrylate, di-vinyl benzene and methacrylic acid. Closer examination of the composition reveals an architecture consistent with that of a polymeric stabilizer suitable for use as an inverse emulsion (water-in-oil) stabilizer. This analysis of the disclosed xe2x80x9cvinylxe2x80x9d polymer is even more interesting in light of previous work done by Xerox.
In 1977 John Pacansky claimed a stabilized alcohol or water-in-oil ink emulsion including in part of 20-40% of a resin having polar segments which were miscible with alcohol/water and non-polar segments which were miscible in the non-polar phase of the ink (J. T. Pakansky, U.S. Pat. No. 4,059,554 (1977)). Pacansky suggested that the use of polymeric stabilizers could overcome difficulties associated with controlling the meta-stability of the ink emulsions previously stabilized with surfactants. Poorly stabilized ink/alcohol emulsions were observed to have broken down while standing (i.e. shelf-life stability) and/or prematurely on the ink rollers. However, extremely stable emulsions tended to give poor printing results (i.e. high background/toning).
Pacansky also preferred the use of relatively small polyhydric alcohols such as ethylene glycol and the like, evn though polyhydric alcohols have been the preferred hydrophilic phase for lithographic ink emulsions for many years according to patent literature.
In 1974, Alexander Spencer and Alfred Spicer (Gestetner) obtained a patent for a lithographic printing ink that was produced by suspending ink in a hydrophilic medium that was characterized by a specific viscosity and rheology profile (A. Spencer and A. L. Spicer, U.S. Pat. No. 3,803,070 (1974)). It was claimed that a separate fountain solution was unnecessary. Spencer and Spicer preferred the use of liquid polyhydric alcohol (i.e. ethylene glycol) alone or in combination with water and optionally hydrophilic phase rheology modifiers. It was also suggested that it might be advantageous to include a spreading agent such as acetone, isopropyl alcohol or ethanol in the hydrophilic phase.
In 1977, H. B. Parkinson patented a composition for a single step lithographic ink which also utilized small polyhydric alcohols (H. B. Parkinson, U.S. Pat. No. 4,045,232 (1977)).
This particular invention related the use of acid treated resins in combination with polyhydric alcohol to generate a lithographic ink with specific rheology. Parkinson claimed that the strong mineral acid treatment of the ink resin imparted the improved properties in this field. De Santo et al. also claimed the use of acid in a single fluid type ink system (R. F. De Santo, S. S. Carava, H. B. Parkinson, U.S. Pat. No. 4,981,517 (1991)).
In this case phosphoric acid was claimed as a stabilizer. The other important features of their invention composition included a diluent with properties similar to fuel oil (No 1, No 2) and a polyol (i.e. ethylene glycol).
Polyhydric alcohols are preferred over water ink emulsions for various reasons not the least of which is the fact that these types of molecules do not evaporate as fast as water. However, a combination of water and polyhydric alcohols are claimed in most cases.
The ink emulsion patent literature contains examples of dispersed phases that were ultimately more complex than just a single polyhydric alcohol and/or a combination of a polyol and water. Hydrophilic phases used in ink emulsions optionally contain a) water b) polyhydric alcohols c) rheology modifiers d) desensitizer/phosphoric acid e) wetting agents f) hygroscopic agents g) anti-corrosive agents h) pH buffers i) surfactants j) chelating agents k) water soluble polymers.
Recently, Ohshima et al. patented an ink emulsion system which relates the use of an emulsified UV cure compound as well as a hygroscopic compound, glycol, triethanol amine and low HLB surfactant (K. Ohshima, M. Imamura, K. Taniguchi, E. Kawamura, H. Adachi, U.S. Pat. No. 6,063,835 (2000)). In this case, the dispersed phase of the emulsion was preferred to be 60-80% by weight. The importance of, and the interest in, the dispersed phase composition is readily apparent. However, the previous work discussed above is lacking with respect to the dispersed phase relative affinity for lithographic plate non-image area.
U.S. Pat. No. 5,714,300 discloses two-layer systems in which the lower layer is a crosslinked hydrolyzed tetraalkyl orthosilicate hydrophilic polymer and the top layer is a negative diazo composition having at least two diazo compounds. In contrast, in the present invention, the lower layer is crosslinked, for example, with zirconium ammonium carbonate, formaldehyde or other non-orthosilicate compounds.
U.S. Pat. No. 5,776,653 discloses a system similar to that disclosed in U.S. Pat. No. 5,714,300 except that the plates are developed on press by wiping with disposable absorbing tissue moistened with water or fountain solution. U.S. Pat. No. 5,776,654 is similar to U.S. Pat. No. 5,776,653 except that the plates are developed on press by fountain solution. U.S. Pat. No. 5,922,511 is similar to U.S. Pat. No. 5,776,654.
The U.S. Pat. Nos. 6,182,569; 6,182,570; and 6,192,798 disclose multi-layer systems, at least one of which is characterized by ablative absorption of laser radiation.
Conventional lithographic plate and ink combinations do not have the ability to provide clean lithographic printing in the absence of fountain solution added on press.
The present invention has utility in single fluid lithography. More particularly, the imageable element according to the present invention can be used advantageously with one fluid offset printing inks and in the preparation of lithographic printing plates that are suitable for use in one fluid offset printing.
Successful single fluid lithography hinges, at least in part, on the ability of the dispersed hydrophilic phase in an ink emulsion to protect the non-image area of the printing plate from ink deposition (i.e. toning, scuming). Therefore, the dispersed phase-non image area interaction and its optimization becomes increasingly important when no additional hydrophilic material (i.e. water, fountain solution) is added on press as is the case with single fluid lithography.
Common difficulties encountered by practitioners of lithography include the poor solubility of the layer components in the solvents selected for the preparation of the coating solutions, insufficient differentiation between the image areas and the non-image areas, poor developability, undesirable scumming during printing, low practical light-sensitivity, poor adhesion of the imaging layer, low resistance to delamination under humid conditions, poor resistance to press chemicals, ablation of the imageable layer and short press life.
Accordingly, it is an object of the present invention to provide an imagable element that has an ablation free imageable ink-receptive layer, which enables the coating edges to be maintained under prolonged development conditions in aggressive developers with little or no loss of the unexposed imageable composition, thereby providing superior press life, resistance to plate chemicals and resistance to scumming and toning of the non-image areas during printing.
The present invention provides such an imageable element, which is suitable for printing with single fluid inks
The present invention provides an imageable element, including:
a substrate;
a crosslinked layer disposed on the substrate; wherein the crosslinked layer is formed from a polyfunctional crosslinkable resin and a crosslinking agent selected from the group consisting of: a polyvalent metal salt, a polyvalent metal complex, an amino resin crosslinking agent, an amido resin crosslinking agent, an aldehyde crosslinking agent and a combination thereof; and
an imageable ink-receptive layer disposed on the crosslinked layer, the imageable ink-receptive layer including an ablation free imageable composition.
The present invention also provides an imageable element, including:
a substrate;
a crosslinked layer disposed on the substrate; and
an imageable ink-receptive layer disposed on the crosslinked layer, the imageable ink-receptive layer including an ablation free imageable composition selected from the group consisting of:
a hydroxyfunctional resin including a covalently bound radiation sensitive group capable of increasing the solubility of the imageable composition in an alkaline developer upon exposure to radiation and an isocyanate crosslinking agent;
a thermally sensitive polymer which exhibits an increased solubility in an aqueous developer solution upon heating, the thermally sensitive polymer including at least one covalently bonded unit and at least one thermally reversible non-covalently bonded unit, which includes a two or more centered H-bond within each the non-covalently bonded unit;
a crosslinkable, polyfunctional alkali-soluble polymer and a divinyl ether;
an acid curable composition, an acid generator and optionally, a photothermal converter;
an aromatic diazonium salt containing compound;
a free radical polymerizable composition comprising a polymerizable polyfunctional ethylenically unsaturated compound, a free radical generator and optionally a monofunctional ethylenically unsaturated comonomer;
a crosslinkable composition comprising a polymerizable polyfunctional ethylenically unsaturated compound and optionally a photosensitizer; and
a composition comprising an aromatic diazonium salt containing compound, a polymerizable polyfunctional ethylenically unsaturated compound and at least one of a free radical generator and a photosensitizer.
The present invention further provides a method of producing an imaged element including the steps of:
providing an imageable element, including: a substrate; a crosslinked layer disposed on the substrate, wherein the crosslinked layer is formed from a polyfunctional crosslinkable resin and a crosslinking agent selected from the group consisting of: a polyvalent metal salt, a polyvalent metal complex, an amino resin crosslinking agent, an amido resin crosslinking agent, an aldehyde crosslinking agent and a combination thereof; and an imageable ink-receptive layer disposed on the crosslinked layer, the imageable ink-receptive layer including an ablation free imageable composition;
optionally subjecting the imageable ink-receptive layer to reaction conditions sufficient to produce an imageable crosslinked element having a crosslinked ink-receptive layer;
imagewise exposing the crosslinked imageable element to radiation to produce an imagewise exposed element having exposed and unexposed regions; and
contacting the imagewise exposed element and a developer to produce the imaged element.
The present invention still further provides a method of producing an imaged element. The method includes the steps of:
providing an imageable element including a substrate, a crosslinked layer disposed on the substrate and an imageable ink-receptive layer disposed on the crosslinked layer, the imageable ink-receptive layer including an ablation free imageable composition selected from the group consisting of: a hydroxyfunctional resin including a covalently bound radiation sensitive group capable of increasing the solubility of the imageable composition in an alkaline developer upon exposure to radiation and an isocyanate crosslinking agent; a thermally sensitive polymer which exhibits an increased solubility in an aqueous developer solution upon heating, the thermally sensitive polymer including at least one covalently bonded unit and at least one thermally reversible non-covalently bonded unit, which includes a two or more centered H-bond within each the non-covalently bonded unit; a crosslinkable, polyfunctional alkali-soluble polymer and a divinyl ether; an acid curable composition, an acid generator and optionally, a photothermal converter; an aromatic diazonium salt containing compound; a free radical polymerizable composition comprising a polymerizable polyfunctional ethylenically unsaturated compound, a free radical generator and optionally a monofunctional ethylenically unsaturated comonomer; a crosslinkable composition comprising a polymerizable polyfunctional ethylenically unsaturated compound and optionally a photosensitizer; and a composition comprising an aromatic diazonium salt containing compound, a polymerizable polyfunctional ethylenically unsaturated compound and at least one of a free radical generator and a photosensitizer;
optionally subjecting the imageable ink-receptive layer to reaction conditions sufficient to produce an imageable crosslinked element having a crosslinked ink-receptive layer;
imagewise exposing the crosslinked imageable element to radiation produce an imagewise exposed element having exposed and unexposed regions; and
contacting the imagewise exposed element and a developer to produce the imaged element.
The present invention further still provides a method of producing an inked image including:
providing an imaged element including a substrate, a crosslinked layer disposed on the substrate and an imageable ink-receptive layer disposed on the crosslinked layer, wherein the imageable ink-receptive layer includes an ablation free imageable composition;
imagewise exposing the imageable element to radiation to produce an imagewise exposed element having exposed and unexposed regions;
optionally contacting the imagewise exposed element and a developer to produce the imaged element; and
contacting the imaged element and an emulsion ink to provide an inked image for printing.
The present invention still further provides an imaged element produced by the above method.
The present invention provides an imageable element that has an ablation free imageable ink-receptive layer, which enables the coating edges to be maintained under prolonged development even in aggressive developers with little or no loss of the unexposed imageable composition.
Further, the imageable element according to the present invention provides superior press life and chemical resistance to plate chemicals.
Further still, like silicone waterless plates, the imageable element according to the present invention avoids fountain solution thereby minimizing environmental problems and printing cost by reducing paper waste.
The imageable element according to the present invention is also cost-effective because it requires less manpower due to easy operation and automation and, compared to silicone plates, the plates prepared from the imageable element according to the present invention are less expensive to make and can be used for printing on more varieties of papers, including newspaper paper.